JPH01208971A - Image pickup device - Google Patents

Abstract

PURPOSE:To attain an image pickup even when an object luminance is low at night by selecting for an autofocus either of a measurement means or a peak value detection means in accordance with a object condition. CONSTITUTION:A control circuit 10 obtains the extension position of an image pickup lens 1 through measurement information from a measurement circuit 12 and the present position information of the image pickup lens 1 from a lens position detection circuit 6 and drives the image pickup lens 1. On the other hand, a video signal which is photoelectric-converted in a CCD 3 and obtained is fetched into an AF signal processing circuit 9 and the detection of the peak value of the signal of a high frequency component is executed. When a peak detection failure signal from the AF signal processing circuit 9 is outputted or when a signal calling an attention to use a stroboscope is outputted from a photometry circuit 11, the control circuit 10 executes a driving control (AF control) from the beginning to the end of the image pickup lens 1 based on a signal from the measurement circuit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to improvements in so-called imaging devices such as electronic cameras that perform autofocus control using video signals from an imaging device such as a COD.

(Background of the Invention) Conventional devices of this type have a problem in that autofocus (AF) control is difficult under low illumination conditions such as night photography. This point will be explained in detail below.

Since the AF detection signal is usually a signal obtained by passing a video signal from an image sensor through a high-pass bandpass filter, the signal level is proportional to the spatial frequency within the angle of view and the illuminance of the subject. FIG. 3 shows the relationship between the focus ring position of the lens and the high-frequency component output from the image sensor, which is an AF detection signal, and the peak position of the waveform is the focus position of the focus ring, that is, the focus position of the lens. Here, if (a) is the output signal waveform of a normal object, then (b) is the output signal waveform of an object with low illuminance and low spatial frequency, and the waveform is gentle and peak detection is difficult. (c) is an output signal waveform of a subject with high illuminance and high spatial frequency, the waveform is saturated, peak detection is difficult, and AF sub-control is impossible.

As a countermeasure to the above problem, there is a method of controlling the gain of the output signal, which makes it possible to align the waveform to some extent without depending on the subject conditions. In this case, A
F sub-control becomes impossible, and this type of photography cannot be performed even if an auxiliary light such as a strobe is prepared. In this case, it is conceivable to irradiate infrared light with an infrared light irradiation member attached to a strobe etc. and perform AF sub-control based on the video signal, but generally there is an infrared light cut filter in the optical path in front of the image sensor. , it is difficult to perform AF sub-control using video signals in the infrared region.

(Objective of the Invention) An object of the present invention is to provide an imaging device that solves the above-mentioned problems and is capable of photographing even when the subject illuminance is low, such as at night.

(Features of the Invention) In order to achieve the above object, the present invention projects a signal wave toward a subject, detects a reflected wave of the signal wave from the subject, and detects distance information to the subject. a distance measuring means; an autofocus means for performing autofocus control based on a signal from the distance measuring means or the peak value detecting means; A selection means for selecting either one for autofocus is provided, and when shooting at night, etc., when peak value detection is impossible, an active type that enables distance measurement even under such conditions is provided. The present invention is characterized in that autofocus control is performed based on a signal from a distance measuring means.

(Embodiment of the invention) FIG. 1 is a block diagram showing an embodiment of the invention.
2 is an imaging lens, 2 is an aperture and a shutter, 3 is a CCD which is an imaging element, 4 is an imaging signal processing circuit, 5 is a recording circuit for recording video signals on a magnetic disk, etc., and 6 is the current position of the imaging lens 1. A lens position detection circuit that detects the
7 is a lens drive circuit that drives the imaging lens 1 in its optical axis direction, 8 is a COD drive circuit that drives the CCD 3, 9 is an AP signal processing circuit, 10 is a control circuit, 11 is a photometry circuit, and 12 is an imaging circuit. The AP signal processing circuit 9 is used to determine the initial movement direction of the lens 1, and when the AP signal processing circuit 9 outputs a peak detection impossible signal or when the photometry circuit 11 outputs a signal prompting the use of a strobe. An active type ranging circuit used instead, 13 is a strobe, and 14 is an AF selection switch.

FIG. 2 shows the configuration of the distance measuring circuit 12.
1 is an infrared light emitting element that projects infrared light through a projection lens 22; 23 is a light receiving lens 24 that receives the infrared light from a subject;
It is a line sensor that receives light through the

Here, the operation of the distance measuring circuit 12 will be briefly explained.
The baseline length is known, and then infrared light is projected from the infrared light emitting element 21, and this infrared light is received by the line sensor 23, so that the angle θ becomes clear, and from these, the subject distance R is calculated ( R=L/tanθ).

Next, AP operation will be explained.

The active type distance measuring circuit 12 uses triangular distance measurement as described above, and can obtain distance measurement information to the subject. A control circuit 10 for controlling various operations of the camera determines whether the imaging lens 1 should be extended or At this point, the initial movement direction of the lens for focusing is determined, and the imaging lens 1 is driven via the lens drive circuit 7. On the other hand, the image signal obtained by photoelectric conversion by the CCD 3 is taken into the AF signal processing circuit 9, where the peak value of the high frequency component signal is detected.
After confirming that the peak value has been detected by the rear limb circuit, the control circuit 10 immediately stops the extension of the imaging lens 1 via the lens drive circuit 7.

When the above operation is completed, the control circuit 10 controls the shutter and the aperture 2, that is, performs exposure control.

As a result, the video signal photoelectrically converted by the CCD 3 and subjected to exposure control by the shutter and diaphragm 2 passes through the imaging signal processing circuit 4, and is then finally recorded by the recording circuit 5 onto a magnetic disk or the like.

In addition, in the above operation process, if a peak detection impossible signal is output from the AF signal processing circuit 9, or if the photometry circuit 1
1 outputs a signal prompting the use of a strobe, the control circuit 10, based on the signal from the distance measuring circuit 12,
Not only the initial movement direction of the lens for focusing, but also the extension amount control of the imaging lens 1, that is, the driving control (AP amount control) of the imaging lens 1 from the beginning to the end.Then, the strobe 14 is made to emit light, and the following steps are performed. Have them do the same thing.

The above AP amount control switching is performed using the AP selection switch 1.
4 can also be performed by external operation. Also, the reason why the drive control of the imaging lens 1 to the end is not performed based on the information from the distance measuring circuit 12 during normal shooting is as follows.
This is because an active type AP has a limit in distance detection, and is not preferable in terms of accuracy in a camera having a lens with a large focal length. In addition, in the case of the beak detection method, the position and size of the distance measurement field of view can be changed freely, making it possible to achieve intelligence.

In addition, since the system uses a method that determines the initial lens movement direction of the imaging lens 1 based on information from the distance measurement circuit 12, it is difficult to move the imaging lens 1 toward the front bin or the rear bin as in the conventional case. This eliminates the problem of hunting occurring due to the necessity of operation, and of the time required to drive the imaging lens 1 to a desired position.

(Correspondence between the invention and the embodiments) In this embodiment, the AP signal processing circuit 9 serves as the peak value detection means of the present invention, the distance measuring circuit 12 serves as the distance measuring means, and the lens drive circuit 7. The COD drive circuit 8 and the control circuit 10 correspond to autofocus means, and the control circuit 10 or the AF selection switch 14 corresponds to selection means.

(Effects of the Invention) As described above, according to the present invention, a signal wave is projected toward a subject, and a reflected wave of the signal wave from the subject is detected to detect distance information to the subject. a distance measuring means; an autofocus means for performing autofocus control based on a signal from the distance measuring means or the peak value detecting means; A selection means for selecting either one for autofocus is provided, and when shooting at night, etc., when peak value detection is impossible, an active type that enables distance measurement even under such conditions is provided. Since autofocus control is performed based on the signal from the distance measuring means, it is possible to take pictures even when the illuminance of the subject is low, such as at night.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing the configuration of the distance measuring circuit shown in Fig. 1, and Fig. 3 shows the focusing position of the lens and the high frequency of the video signal in this type of device. FIG. 3 is a diagram showing the relationship between component outputs. 1...Imaging lens, 3...-CCD, 6
... Lens position detection circuit, 7... Lens drive circuit, 8... COD drive circuit, 9-...
...AF signal processing circuit, 1゜...control circuit,
12... Distance measurement circuit, 14... AF selection switch. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] (1) In an imaging device equipped with a peak value detection means for detecting the peak value of a high frequency component in a video signal from an imaging means, a signal wave is projected toward a subject, and a reflected wave of the signal wave from the subject is detected. a distance measuring means for detecting distance measurement information to the subject, an autofocusing means for performing autofocus control based on a signal from the ranging means or the peak value detecting means, and subject conditions at that time. An imaging apparatus comprising: a selection means for selecting either the distance measuring means or the peak value detection means for autofocus according to the above.